1. Field of the Invention
This invention relates to an improvement in a turbocharger for an intermittent combustion (IC) internal combustion engine and a process therefor, and more specifically to an improved turbine housing unit for said turbocharger which is fabricated from a lay-up or molding of carbon--carbon composite materials.
2. Description of the Related Art
Many intermittent combustion (IC) reciprocating engines are equipped with turbochargers, to improve engine efficiency. Typically, turbochargers consist of three principal components: a turbine, a compressor, and a turbine housing unit. In operation, the turbine captures high-temperature gases coming from the engine exhaust manifold. These exhaust gases then are used to drive a compressor which, in turn, pumps high pressure air into the engine's inlet and compression chambers.
The effect of this process in a gasoline engine is to increase the volume of air available for combustion. Because more air is available, a correspondingly greater amount of fuel can be consumed, or burned, per cycle. In theory, the greater the fuel burned, the greater the horsepower. For diesel engines, the expansion of the high-temperature exhaust gases through the turbine connected to the compressor leads to more efficient operation because the inlet air charge is also increased leading to a higher compression ratio in the compression chambers. As these high-temperature exhaust gases would otherwise be expelled from the engine through an exhaust system, capturing and using the kinetic and thermal energy from the exhaust gases increases overall engine efficiency and horsepower. In an expansion cycle, the exhaust gas turbine can also be coupled to the engine drive train to increase cycle efficiency.
Internal combustion reciprocating engines used for aerospace, military, and transportation applications must be lightweight and capable of operating at elevated temperatures and pressures. Under the current state-of-the-art, turbocharger turbine housing units and gas exhaust manifolds for gasoline and diesel engines are made of steel, cast iron, Ni-resistant iron, or ductile iron with ceramic liners. Turbocharger turbine housing units fabricated from steel or iron are relatively heavy. Excessive weight is detrimental to engine efficiency and prohibitive in aerospace applications. Hence, a lightweight alternative to steel or iron turbine housing units would be a highly desired improvement in the prior art.
Likewise, steel and iron inherently possess excessive thermal conductivity which increases heat energy loss. As the captured gas heat energy dissipates, less energy is available to drive the turbocharger turbine, thereby reducing the performance and efficiency of the turbine. In addition, in compound diesel engines, the heat energy loss of the high-temperature exhaust gases reduces cycle efficiency. Consequently, a less thermally conductive substitute for steel or iron would be a highly-desired improvement in the prior art.
While Ni-resistant iron is lighter than steel or cast iron, it is very expensive. Likewise, ductile iron is lighter than steel or cast iron, yet it remains relatively heavy overall. A further disadvantage of ductile iron turbocharger turbine housing units is disclosed in U.S. Pat. No. 5,456,578 (Honda et al.). According to Honda et al., "w!hen ductile iron material is used for a turbine housing !, the surface of the ductile housing is oxidized and deteriorated by the heat of the high-temperature exhaust gas." In some instances such deterioration exerts "an especially great influence on engine! efficiency" either because the clearance between the turbine rotors and the turbine housing unit allows the high-temperature gases to escape, or because the turbine housing unit itself is "insufficiently sealed." Therefore, a lightweight alternative to steel and iron turbine housing units which is neither oxidized nor deteriorated by the heat of the high-temperature engine exhaust gases would be a highly-desired improvement in the prior art.